Method and Plant for Thermal Conversion of Solid Fuels

ABSTRACT

The invention relates to thermal conversion of solid fuels with a low organic content and can be used in the fuel-processing industry. Conversion of oil shale or high-ash solid fuels comprises flue-gas drying of feedstock, recovering the solid phase as a heat-carrying agent, feedstock pyrolysis in a reactor, separating a gas-vapour mixture from the coke-ash residue in a dust-settling chamber, discharging ash, cooling flue gases, and combustion of the coke-ash residue. An inert material having an ambient temperature is supplied to the outlet of the coke-ash residue ignition chamber. The plant comprises, arranged in series, a reactor, a dust-settling chamber, a flash-process furnace, a heat-carrier cyclone, an ash cyclone, a waste-heat recovery system, an ash-discharge system and a bin for inert material connected to the outlet of the coke-ash residue ignition chamber. The invention allows for a more complete use of the oil shale energy potential and for obtaining ash with a reduced negative effect on the environment, which makes it possible to use the ash for recultivation of quarries resulting from oil shale mining.

RELATED APPLICATIONS

This Application is a Continuation application of InternationalApplication PCT/RU2016/000793, filed on Nov. 30, 2016, which in turnclaims priority to Russian Patent Applications No. RU2015153090, filedDec. 10, 2015, both of which are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The invention relates to thermal conversion of solid fuels with a loworganic content, e.g., oil shale, and can be used in the fuel-processingindustry at production of a liquid or gaseous fuel, or an alternativefuel to substitute oil.

BACKGROUND OF THE INVENTION

There is a known method and a plant for its implementation (StelmakhG.N., Tyagunov B.N., et al. Electric process plant for conversion offine-grained oil shale. Oil shale, No. 2/2, 1985, pp. 189-196).

The method comprises drying of ground fuel with a gaseous drying agent,pyrolysis of dried fuel with a solid heat-carrying agent with generationof vapour gases and coke-ash residue, burning the latter in a heated airflow with formation of gas suspension, staged separation of the gassuspension into an ash heat-carrying agent to be returned to thepyrolysis stage, ash to be fed to cooling and withdrawn from theprocess, and flue gases to be fed to after-burning and later used as agaseous drying agent.

The plant for implementation of this method comprises, arranged inseries, a flash-process drier, a waste drying agent separator, apyrolysis reactor, its inlet connected to the fuel discharge branch pipeof the waste drying agent separator, a flash-process furnace, a soliddrying agent separator, its dust discharge branch pipe connected to thereactor inlet, a drying agent separator, an ash cooler connected to theash discharge branch pipe of the drying agent separator, and a recoveryboiler, its inlet connected to the gas exhaust branch pipe of the dryingagent separator, and its outlet connected to the flash-process drier.

The disadvantage of the method lies in that after-burning of flue gasesin the recovery boiler at a α<1 results in incomplete oxidation ofcombustible components contained therein, and hence, to pollution of theenvironment with products of incomplete combustion of organic fuels.Pollution of the environment is also contributed to by the fact that, inthe course of drying in the flash-process drier, some of the fuelparticles are overheated, which results in bertinization products(carbon monoxide, hydrogen sulphide, carcinogenic substances, etc.)coming into the waste drying agent, thus polluting the environment.

There is also known a method and a plant for thermal conversion of oilshale (see RF patent No. 1766949, priority of Jun. 04, 1990, IPC C10B53/06).

The method comprises drying of fuel with a gaseous drying agent,separating the fuel from the waste drying agent, pyrolysis of dried fuelwith circulating solid heat-carrying agent with generation of vapourgases and coke-ash residue, burning the latter and formation of gassuspension, staged separation of the latter into a circulatingheat-carrying agent to be returned to the pyrolysis stage, a gaseousdrying agent to be fed to the drying stage, and an ash-and-smokemixture, cooling this mixture and separating the same into ash to bewithdrawn from the process and flue gases to be fed to the drying stage.

The plant for implementation of this method comprises, arranged inseries, a flash-process drier, a waste drying agent separator, apyrolysis reactor, its inlet connected to the fuel discharge branch pipeof the waste drying agent separator, a flash-process furnace, a soliddrying agent separator, its gas exhaust branch pipe connected to thedrier inlet, an ash-and-smoke mixture cooler and an ash separator, itsgas exhaust branch pipe connected to the smoke exhauster and further tothe flash-process drier.

The disadvantage of the method lies in that no after-burning is providedfor flue gases of the flash-process furnace, which results in pollutionof the environment with products of incomplete combustion.

The closest to the claimed invention are the method and plant forthermal conversion of high-ash fuels (see RF invention No. 2118970,priority of Apr. 25, 1997, IPC C10B 53/06, C10B 49/18).

The method is implemented as follows. The fuel is dried in a drier, thenthe fuel is separated from the waste drying agent in the separator andis pyrolyzed in a pyrolysis reactor. The generated coke ash residue isburnt in a flash-process furnace. The gas suspension obtained afterburning is subjected to staged separation in separators into a solidheat-carrying agent, a gaseous drying agent and an ash-and-smokemixture, which is cooled in a cooler and is separated in a separatorinto ash and flue gases. A part of the flue gases is recirculated to thestage of cooling the ash-and-smoke mixture, with the concentration ofsolid particles in this mixture maintained by adjusting the flow rate ofrecirculating flue gases. The remaining part of the flue gases is burntin a recovery boiler along with the waste drying agent, with thetemperature at the drying stage maintained by adjusting the flow rate ofthe flue gases being burnt.

The disadvantage of this method and plant is that to ensure regulatingthe quantity of the material being fed and the temperature it isnecessary to install additional equipment, e.g., a heat exchanger, or aseparator, which complicates the arrangement. Besides, delivering a partof ash at the temperature of 250-600° C. complicates handling theprocess, as it requires accuracy in feeding a loose material at aconstant temperature: feeding a loose material at a temperature below250° C. may result in termination of the burning process, while limitingthe minimum ash temperature to 250° C. would result in larger amounts ofthe material fed and, as a consequence, a larger volume of the furnacecombustion chamber, as well as larger dimensions of equipment forseparation of the heat-carrying agent and ash.

SUMMARY OF THE INVENTION

The objective of the proposed invention is to ensure temperature controlin the flash-process furnace and to reduce the overall dimensions andmetal consumption of equipment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic illustration of a device for converting oilshale or high-ash solid fuels.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The method for conversion of oil shale or high-ash solid fuels comprisesflue-gas drying of feedstock, recovering the solid phase as aheat-carrying agent, feedstock pyrolysis in a reactor, separating agas-vapour mixture from the coke-ash residue in a dust-settling chamber,discharging ash, cooling flue gases, and combustion of the coke-ashresidue. Here, an inert material having an ambient temperature issupplied to the outlet of the coke-ash residue ignition chamber fortemperature control in the flash-process furnace, and ash from the ashdischarge system with a temperature of 10 to 200° C. is used as an inertmaterial.

The plant for implementation of this method comprises, arranged inseries, flash-process drier 1, waste drying agent separator 2, pyrolysisreactor 3, its inlet connected to fuel discharge branch pipe of thewaste drying agent separator, flash-process furnace 5, solid dryingagent separator 6, its gas exhaust branch pipe 7 connected to the drierinlet, ash-and-smoke mixture cooler 8 and ash separator, its gas exhaustbranch pipe connected to the smoke exhauster and further to theflash-process drier. The plant operates as follows.

The shale ground to 0-25 mm is fed with an auger to flash-process drier1, where the shale is dried with exhaust flue gases. Next, the gassuspension of shale and the flue gases is fed to the dry shale cyclonefor separation of the solid phase. Upon being mixed with the circulatingash heat-carrying agent, the dry shale is fed to reactor 3, wherepyrolysis of the organic part of the shale occurs at temperatures450-550° C. The pyrolysis products in the vapour phase and the mixtureof the circulating heat-carrying agent with the mineral part of theshale are fed to dust-settling chamber 4. The vapours of pyrolysisproducts are fed to condensation (not shown in the diagram), wherepurification, fractionation, and cooling take place, and the targetproducts are released (shale oil and pyrolysis gas).

The mixture of the circulating heat-carrying agent with the mineral partof the shale (coke-ash residue) from dust-settling chamber 4 is fed withan auger to flash-process furnace 5. Air is fed to the lower part of theflash-process furnace to ensure burning of organic matter in thecoke-ash residue and to enable the flash drying process.

The gas suspension of combustion products, nitrogen and the solid phaseis fed from the upper part of the flash-process furnace to theheat-carrying agent separator, wherefrom a part of the solid phase isreturned to reactor 3. Further on, the gas suspension from the separatorcomes into ash cyclone 6, where it is separated into ash and flue gas.The flue gas is fed to heat recovery (recovery boilers) and intoflash-process drier 1, where it gives heat to the shale drying processand further, after cyclone 2, is discharged through a filtration systeminto the atmosphere.

The ash from cyclone 6 is cooled down in an ash heat exchanger to thetemperature of ˜80-120° C., and is then fed to humidification andfurther on to recovery. As distinct from the prototype, a part of theash, prior to its humidification, is fed at the temperature 80-120° C.with an auger to the flash-process furnace to the outlet from theaccelerating section of the furnace. Here, the coke-ash residue from thedust-settling chamber has been ignited, and delivering the ash enablesto regulate the temperature in the furnace. Feeding “cold” ash at thetemperature of 80-250° C. makes possible to increase the air flow toensure the fluid dynamics of the spouted bed and to increase theair/combustibles ratio above 1, which ensures more thorough combustionof fuel in the coke-ash residue.

Therefore, the invention allows for a more complete use of the oil shaleenergy potential and for obtaining ash with a reduced negative effect onthe environment, which makes it possible to use the ash forrecultivation of quarries resulting from oil shale mining.

What is claimed is:
 1. A method for converting oil shale or high-ashsolid fuels comprising: flue-gas drying of feedstock; recovering a solidphase as a heat-carrying agent; performing feedstock pyrolysis in areactor; separating a gas-vapor mixture from a coke-ash residue in adust-settling chamber; discharging ash, cooling flue gases, andcombusting the coke-ash residue; and controlling temperature in aflash-process furnace by supplying an inert material having an ambienttemperature to an outlet of a coke-ash residue ignition chamber.
 2. Themethod according to claim 1, wherein the inert material is ash from adischarge system, the ash having a temperature of 10 to 200° C.
 3. Adevice for converting oil shale or high-ash solid fuels comprising:arranged in series a reactor, a dust-settling chamber, a flash-processfurnace, a heat-carrier cyclone, an ash cyclone, a waste-heat recoverysystem, an ash-discharge system, wherein a bin for inert material isconnected to an outlet of a coke-ash residue combustion chamber fortemperature control in an ignition chamber of the flash-process furnace.